1. Field of the Invention
The present invention relates to a monolithic ceramic electronic component and a method for manufacturing the monolithic ceramic electronic component and, in particular, to a monolithic ceramic electronic component in which external electrodes are directly formed on the surface of a laminate by plating and a method for manufacturing the monolithic ceramic electronic component.
2. Description of the Related Art
As illustrated in FIG. 5, a monolithic ceramic electronic component 101, such as a monolithic ceramic capacitor, includes a laminate 102, which includes ceramic layers 103 and internal electrodes 104 and 105 alternately disposed between the ceramic layers 103. An end of each of the internal electrodes 104 is exposed at an end surface 106 of the laminate 102. An end of each of the internal electrodes 105 is exposed at an end surface 107. External electrodes are provided on the end surfaces 106 and 107 to electrically connect the corresponding ends of the internal electrodes 104 and 105.
In general, the external electrodes are formed as follows: first, a metal paste including a metal component and a glass component is applied to the end surfaces 106 and 107 of the laminate 102 and is baked to form paste electrode layers 108 and 109. First plated layers 110 and 111 made primarily of, for example, Ni, are then formed on the paste electrode layers 108 and 109. Second plated layers 112 and 113 made primarily of, for example, Sn, are then formed on the first plated layers 110 and 111. Thus, the external electrodes include the paste electrode layers 108 and 109, the first plated layers 110 and 111, and the second plated layers 112 and 113.
The external electrodes are required to have excellent solder wettability so that the monolithic ceramic electronic component 101 can be soldered to a substrate. The external electrodes are also required to electrically connect the corresponding internal electrodes, which are insulated from each other. The second plated layers 112 and 113 provide excellent solder wettability to the monolithic ceramic electronic component 101. The paste electrode layers 108 and 109 electrically connect the internal electrodes 104 and 105. The first plated layers 110 and 111 prevent solder leaching.
However, the paste electrode layers 108 and 109 have a thickness of several tens to several hundreds of micrometers. Thus, in a monolithic ceramic electronic component 101 having a given specified volume, the paste electrode layers 108 and 109 disadvantageously reduce the effective volume for capacitance. In contrast, the first plated layers 110 and 111 and the second plated layers 112 and 113 have a thickness off only several micrometers. Accordingly, if the external electrodes include only the plated layers, the effective volume for capacitance can be increased.
For example, Japanese Unexamined Patent Application Publication No. 63-169014 discloses a method for depositing an electroconductive metal layer by electroless plating on side surfaces of a laminate at which internal electrodes are exposed so that the exposed internal electrodes are connected to each other.
An example of a monolithic ceramic electronic component described in Japanese Unexamined Patent Application Publication No. 63-169014 is a monolithic ceramic capacitor in which side surfaces of a laminate at which Ni-based internal electrodes are exposed are directly coated with Cu.
However, in this method, a plating solution tends to enter the laminate from the side surfaces at which the internal electrodes are exposed. When the laminate is heated at about 800° C. to remove water in the plating solution, Cu in a plated layer may be significantly diffused along the internal electrodes, causing Kirkendall voids in the plated layer. A Kirkendall void having an opening on the surface of the plated layer allows water to enter the laminate, thus causing deterioration in product lifetime under high temperature and high humidity.